Add casting code quality lint scan

Enforce type assertion style by adding a new oxlint scan with `typescript/consistent-type-assertions` rule. Requires using `as const`, type annotations, or `satisfies` instead of raw type casts, with documented `SAFETY:` exceptions for unavoidable cases.

AGENTS.md

@@ -33,6 +33,14 @@ Never use vague names like `helpers`, `utils`, `common`, `misc`, or `shared-stuf
 
 ## Type Declarations: Prefer `.ts` Over `.d.ts`
 
+## Type Assertions: Prefer Checked Types
+
+Avoid type assertions except `as const`. Unavoidable casts need a line-specific `SAFETY:` explanation:
+
+```ts
+// oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: Explain the verified invariant here.
+```
+
 # Verifying Changes
 
 - **Typecheck**: `pnpm tc` (or `tc:node` / `tc:cli` / `tc:web`)

config/oxlint-code-quality-casting.json

@@ -0,0 +1,17 @@
+{
+  "$schema": "../node_modules/oxlint/configuration_schema.json",
+  "plugins": ["typescript"],
+  "categories": {
+    "correctness": "off",
+    "suspicious": "off",
+    "pedantic": "off",
+    "perf": "off",
+    "style": "off",
+    "restriction": "off",
+    "nursery": "off"
+  },
+  "rules": {
+    "typescript/consistent-type-assertions": ["error", { "assertionStyle": "never" }]
+  },
+  "ignorePatterns": ["**/node_modules", "**/dist", "**/out"]
+}

config/scripts/casting-code-quality.test.mjs

@@ -0,0 +1,64 @@
+import { spawnSync } from 'node:child_process'
+import { mkdtempSync, rmSync, writeFileSync } from 'node:fs'
+import path from 'node:path'
+import { expect, it } from 'vitest'
+import { OXLINT_SCANS, diagnosticTouchesAddedLines } from './check-changed-code-quality.mjs'
+import { resolveOxlintInvocation } from './oxlint-cli-invocation.mjs'
+
+const root = path.resolve(import.meta.dirname, '..', '..')
+const oxlint = resolveOxlintInvocation(root)
+const rule = 'typescript(consistent-type-assertions)'
+
+function lint(file, args = []) {
+  const result = spawnSync(
+    oxlint.command,
+    [...oxlint.prefixArgs, ...args, '--format', 'json', file],
+    { cwd: root, encoding: 'utf8', windowsHide: true }
+  )
+  expect(result.error).toBeUndefined()
+  return { status: result.status, diagnostics: JSON.parse(result.stdout).diagnostics }
+}
+
+it.each(['config', 'mobile'])('enforces new casts without changing full lint in %s', (parent) => {
+  const directory = mkdtempSync(path.join(root, parent, 'casting-lint-test-'))
+  const file = path.join(directory, 'fixture.test.ts')
+  try {
+    writeFileSync(
+      file,
+      [
+        "export const oldCast = { current: '⌘N' as string | null }",
+        'export const doubleCast = undefined as unknown as string',
+        "export const annotated: { current: string | null } = { current: '⌘N' }",
+        "export const constant = { current: '⌘N' } as const",
+        "export const checked = { current: '⌘N' } satisfies { current: string | null }",
+        '// oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: Exercise the explicit exception.',
+        'export const justified = undefined as unknown'
+      ].join('\n')
+    )
+
+    const full = lint(file)
+    expect(full.status).toBe(0)
+    expect(full.diagnostics.filter((diagnostic) => diagnostic.code === rule)).toEqual([])
+
+    const scan = OXLINT_SCANS.find((candidate) => candidate.label === 'casting code quality')
+    expect(scan).toBeDefined()
+    const casting = lint(file, scan.args)
+    expect(casting.status).toBe(1)
+    expect(casting.diagnostics).toHaveLength(3)
+    expect(casting.diagnostics.every((diagnostic) => diagnostic.code === rule)).toBe(true)
+
+    const relative = path.relative(root, file).split(path.sep).join('/')
+    const changed = new Map([[relative, [{ start: 2, end: 2 }]]])
+    const findings = casting.diagnostics.filter((diagnostic) =>
+      diagnosticTouchesAddedLines(diagnostic, changed, root)
+    )
+    expect(findings).toHaveLength(2)
+    expect(findings.every((diagnostic) => diagnostic.severity === 'error')).toBe(true)
+
+    writeFileSync(file, 'export const angle = <string>undefined\n')
+    expect(lint(file).status).toBe(1)
+    expect(lint(file, scan.args).diagnostics.map((diagnostic) => diagnostic.code)).toEqual([rule])
+  } finally {
+    rmSync(directory, { recursive: true, force: true })
+  }
+})

config/scripts/check-changed-code-quality.mjs

@@ -15,6 +15,10 @@ export const OXLINT_SCANS = [
     label: 'code quality',
     args: ['--report-unused-disable-directives-severity', 'warn']
   },
+  {
+    label: 'casting code quality',
+    args: ['--config', 'config/oxlint-code-quality-casting.json']
+  },
   {
     label: 'type-aware code quality',
     args: ['--type-aware', '--config', 'config/oxlint-code-quality-type-aware.json']